Physio-biochemical and anatomical responses of upland rice (Oryza sativa L.) genotype during the vegetative stage under drought stress

Upland rice cultivation in highland regions is often challenged by drought, leading to poor seedling growth and low productivity.This study aimed to investigate the physiological, biochemical, and anatomical responses of the Thai rice landrace Nhonkhab under drought and rewatering conditions.After germination, 28-day-old Nhonkhab rice seedlings were deprived of water for 7 days (35 days old) and then rewatered for 5 days (40 days old).Growth, physiological, biochemical and anatomical characteristics of the 35 and 40-day-old seedlings were evaluated.Results showed that drought stress significantly reduced relative water content (RWC) (-36.38%)but was rapidly restored after rewatering (+12.15%) when compared to the control.After drought stress treatment, malondialdehyde (MDA) content and electrolyte leakage (EL) percentage increased (+150% and +59.37%, respectively), indicating oxidative stress and membrane damage.Growth and developmental adaptations, such as elongated roots and curled leaves, facilitated survival during drought, with leaves unfurling post-rewatering.Following rewatering, rice plants exhibited robust recovery, supported by internal structural adaptations such as increasing stomatal density, thickening of the cuticle layer around the midrib and leaf blades, increasing bulliform cells number and size, and modifications in vascular bundles.Principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed distinct patterns in growth, physiological, and anatomical traits across control and treatment groups.These findings provide valuable insights for rice production planning in droughtprone highlands and for selecting or breeding drought-resistant cultivars with improved resilience and productivity.